This invention relates generally to methods and apparatus for forming articles and, more particularly, to a method and apparatus for forming elongated articles having reduced diameter circular cross-sections.
Generally, in the formation of elongate metallic articles having circular cross-sections, the metallic material is compressed above its elastic limit in a chamber and is forced to flow through and take on the shape of a circular opening defined by a die cavity. Such processes are generally termed extrusion, where the material is forced under compression through the die cavity, or drawing, wherein the material is pulled under tension through the cavity. The term "extrusion" will be used hereinafter to refer generally to such processes wherein the material takes on the form of a die cavity. Thus, other material forming processes, such as forging, will be within the scope of this term. Such processes can be used in the production of solid cylindrical extrusions, such as wire, or tubular extrusions, the latter of which are provided by the location of an elongate ram or mandrel in the die cavity.
In present extrusion processes, the work required to be done on the material to deform the same is supplied through either the tensile or compressive forces which are provided during the movement of the metal through the die cavity. However, since the extent of the metal deforming work done by the above-mentioned tensile and compressive forces is, by necessity, limited, the amount of reduction of the circular cross-section of the material is correspondingly limited. Thus, it is frequently necessary to utilize several successive dies in order to obtain an elongate article having a reduced-diameter circular cross-section.